1. Field of the Invention
The present invention relates to the treatment of phosphate ores. More particularly it relates to a selective flocculation process for the treatment of fractions of fine granulometry of phosphate ores with a siliceous-clayey gang.
2. Description of the Prior Art
The treatment of ores generally implies flotation operations, which permit the separation of various minerals present in the crude ore. It is known, for example, the phosphate ores contain apatite mixed with other minerals derived from the gang, for example a siliceous and clayey gangue or a carbonated gangue. Such flotation treatments are widely used in practice for the treatment of course fractions; on the other hand, fine fractions which cannot be treated by flotation could be enriched by selective flocculation. To establish the state of the prior art in this field, one may mention, for example, the article of G. Baudet, M. Morio, M. Rinaudo and H. Nematollahi published in April 1977 in the Revue Industrie Minerale-Mineralurgie, under the title "Synthesis and Characterization of Selective Flocculents based on Xanthated Derivatives of Cellulose and Amylose." This document describes the principal selective flocculation processes.
In the case of phosphate ores, it is well-known that the fine mineral particles contained in the ores present a difficult problem, for it is not known how to separate them by flotation. As a general rule, ore particles having a granulometry higher than 40 .mu.m, for example between 40 and 800 .mu.m are quite suitable for a flotation treatment. Thus, at the present time, a prior separation of the fine fractions of granulometry less than about 40 .mu.m is used, considering that it is not known how to treat them subsequently. In fact, if they were present in the mineral fractions, they would constitute an intolerable handicap for the subsequent processing operations. It follows that these fine fractions are at present discarded and lost, which represents very considerable losses since they can reach close to 40% of the phosphate contained in the extracted ore. At the present time, it is accepted that, with respect to the extracted ore, there is a recovery of only 35 to 70% of the phosphate content, which is a Figure which becomes more and more unacceptable.
It has already been proposed in the prior art to utilize processes to exploit the fines of phosphate ores more completely. One of these representative documents is U.S. Pat. No. 2,660,303 granted in the name of J. F. Haseman, which relates to the flocculation of the colloidal fines in a phosphate ore in the presence of clay. This known process consists firstly of dispersing the particles of ore by means of an agent which is preferably sodium hydroxide.
Other known dispersing agents may be utilized and among them sodium silicate. The essential step of the process consists of flocculating the aqueous suspension of phosphate using a starch as a flocculating agent. However, in the course of the tests from which the present invention has been developed, it was observed that the use of simple starch for flocculating the apatite selectively in phosphate ores with a clayey and siliceous gang did not permit a satisfactory selectivity to be achieved nor a sufficiently high flocculation yield.
The invention relates to a process which enables the above-mentioned drawbacks of the prior art to be overcome.
More particularly it relates to a selective flocculation process for apatite of fine granularity contained in phosphate ores.
It is therefore a principal object of the invention to provide a process which can profit from the ore fractions whose granulometry is less than 40 .mu.m on the average.
it is also an object of the invention to provide a process which may be applied on the industrial scale and which is directly applicable to the treatment of phosphate ores as extracted at the present time.